Area Forecast Discussion
Issued by NWS Blacksburg, VA

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931 FXUS61 KRNK 290722 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 322 AM EDT Thu Sep 29 2016 .SYNOPSIS...
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A strong upper level area of low pressure will remain just west of the mountains today into Friday. This system will combine with a residual stationary front across the region to produce periods of showers and thunderstorms today into Friday night. The low will move northeast, away from the region, resulting in drier weather this weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 240 AM EDT Thursday... Appears another active day in store espcly this afternoon as the upper low to the northwest digs toward the Tennessee Valley and another impulse aloft rotates through from the southwest. This looks to again play tag with the stalled surface low and occluded boundary stuck along the Blue Ridge. Bands of added convection likely to take shape across the eastern half as this occurs per latest Cam solutions with coverage rotating north/northwest into northern sections through the evening. However exactly where this takes place and how fast in question given early showers, and idea that this initial axis will shift east, followed by low clouds that may tend to limit instability later on within low level easterly flow. Think best chances of deeper convection will occur just south of the boundary/triple point and perhaps even out west where will have a band under the upper low arriving late. Although lapses likely to be weaker today unless more heating occurs, added cooling aloft and deeper low level southeast flow turning southwest aloft while strengthening supports added severe hail/wind potential. This espcly along/southeast of the boundary near Highway 460 where shear parameters best. Thus after a likely early morning lull as supported by the latest HRRR expect enough coverage to keep overall likely/cat pops in all except the far sw where a weak dry slot may hold. Highest QPF looks to also reside across the easternmost counties with this axis swinging back toward the Virginia Highlands later today. May add Rockbridge to the watch given pockets of heavier rainfall overnight and possible added training bands today. Highs mostly 70s although could get to around 80 southeast if more sunshine develops, while some spots across the north may get stuck in the 60s if clouds persist. Upper low should begin to pivot slowly north/northeast overnight allowing the eastern conveyor belt of deep moisture/convergence to lift a bit farther to the northeast late ahead of the residual surface front. This may also push somewhat drier air aloft into western sections late as the weak surface low along the Blue Ridge retrogrades back westward, and a secondary cold front edges east across the far west. Appears loss of instability should again help reduce thunder chances after this evening but lingering heavy rain threat likely to continue at least northeast third through late tonight. Therefore keeping a gradient of likely or higher pops mainly along/east of the Blue Ridge overnight and chances elsewhere given expected slower exodus of deeper moisture. Low temps mainly 50s mountains to mid 60s out east.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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As of 230 AM EDT Thursday... A very large closed low will wobble over the southern Ohio Valley through Saturday night. Through each period, precipitation coverage will become smaller and smaller as dry air gets wrapped into this low. Dry air will start moving over the the southern Appalachains Friday morning, then works north through the day. Rain showers will begin to taper off from south to north behind a short wave axis, finally exiting the Alleghany Highlands and the Hill City of Lynchburg late Friday evening. Even though mid and high levels will remain relatively dry Saturday, low level moisture and afternoon heating may produce a few shallow dark base clouds and a few showers. Overall coverage of showers and measurable rain will be less than 10 percent Saturday afternoon. Temperatures will remain seasonal Friday into the weekend with highs ranging in the 70s, some 60s along ridge tops and lows into the 50s.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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As of 320 PM EDT Wednesday... Closed upper low will lift northeast and reach the St. Lawrence river valley by Sunday night. Then, the low center will open up and weaken as it moves across New England Monday and moves into the Atlantic ocean on Tuesday. The exact evolution of the large scale patterns will affect the eventual track of what is forecasted by NHC to be Hurricane Matthew. The storm may threaten the southeast coast next week. This is being monitored by the NHC and WPC. For much of the extended ISC grids leaned towards WPC which was a blend of the 00Z GFS/GEFS MEAN/ECMWF ENS MEAN. Temperatures will start cooler for Saturday with continued improvement as precip/cloudcover comes to an end, then temperatures begin to moderate Sunday into Wednesday.
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&& .AVIATION /07Z THURSDAY THROUGH MONDAY/... As of 1257 AM EDT Thursday... Bands of convection persist across parts of the region tonight, with the best coverage along/east of the Blue Ridge. Expect lingering coverage to perhaps impact all locations excluding KBLF overnight but too iffy to include much more than a VCSH or tempo group through daybreak. Otherwise looking at VFR to MVFR cigs with pockets of IFR mainly around KLYH and where showers/clouds may fade allowing for fog formation to take shape. As an upper low moves south of the Great Lakes Thursday...a cold front will approach the Appalachians from the west. This front will merge with a stationary low pressure system over Virginia on Thursday. This will result in added rounds of showers and storms espcly during the afternoon with perhaps a lull during the morning. Appears cigs may also rise to MVFR to VFR by midday before convection redevelops espcly in a band across the east and another with the front approaching from the west. Still uncertain with overall coverage but given high probability will include a prevailing group in spots with vicinity mention elsewhere. Extended aviation discussion... A deep upper low will remain over the Ohio and Tennessee Valleys through Friday night. This will keep variable clouds, MVFR cigs, and periods of -SHRA across the region through much of the period. Should finally see VFR return during Saturday and continue into Monday as the upper low lifts north and weak high pressure builds in. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Flash Flood Watch through this afternoon for VAZ024-035- 044>047-058-059. NC...None. WV...None.
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&& $$ SYNOPSIS...AMS/JH NEAR TERM...JH SHORT TERM...RCS LONG TERM...KK AVIATION...AMS/JH/WP

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